Brett Stone-Gross*, Christo Wilson*,
Kevin Almeroth*, Elizabeth Belding*, Heather Zheng*,
and Konstantina Papagiannaki**
*Department of Computer Science,
University of California, Santa Barbara
**Intel Research
Pittsburgh, PA
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Connecting to a wireless LAN
◦ Users have become accustomed to protection from
 NATs
 Firewalls
◦ Worms and bots actively scan the Internet for
vulnerable hosts
 Identify machines via port scans
 Attack/Exploit
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Objectives
Motivation & Applicability
Experimental Setup
Identifying Malicious Flows
MAC Layer Impacts
Overall Impacts
Conclusions & Future Work
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To quantify, characterize, and correlate the
effects of malicious traffic flows on a wireless
LAN.
This is the first study to analyze these effects
in a large-scale wireless network
◦ More resource limitations
 Bandwidth
 Channel access
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Improve quality of service offered by wireless
networks
Assist in developing more realistic traffic
models that account for malicious traffic
Applicable to almost any wireless network,
especially those with lax security constraints
including wireless hotspots
Substantiate the need for better wireless
network protections
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◦ Data collection from the 67th IETF meeting in San
Diego, California for a 5-day duration
◦ 44.7Mbps T3 backhaul link
◦ Publicly routable subnet 130.129/16
 No network address translation (NAT)
◦ No firewall/MAC layer encryption
◦ 30 access points
 802.11a/b/g
◦ 11 wireless packet sniffers
 IBM/Toshiba laptops with Atheros chipsets
◦ Wired and wireless traffic captured from a trunk
port on the core router
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Wired Data Set
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Wireless Data Set
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◦ Packet traces from all hosts over all 5 days
◦ 511GB uncompressed
◦ Packet traces from 11 concurrent access points
◦ 131 GB uncompressed
The wired data set was initially utilized to
identify malicious flows and then matched
with the smaller wireless data set
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Port scanning & flooding
Large numbers of short-lived connections
◦ TCP SYNs, ICMP ping
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Well-known exploit signatures
◦ Port-based
◦ Malicious payloads
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Since nearly all connected machines were
laptops, unsolicited incoming connections to
various services were easily identifiable
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HTTP TCP SYN floods
NetBIOS/Microsoft Discovery Services exploits
SSH brute force dictionary attacks
MS SQL exploits
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TCP Statistics
◦ Egress
 4,076,412 out of 272,480,816 (1.5%) were classified as
malicious
◦ Ingress
 2,765,683 out of 284,565,595 (1.0%) were classified as
malicious
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3,906 out of 109,740 unique external IP
addresses (3.6%) engaged in malicious traffic
flows
14 out of 1,786 internal IP addresses (0.8%)
showed indications of malicious activity.
◦ Network experts are more security conscious? 
◦ At least one person was likely infected at the conference
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Not ideal for studying the MAC layer effects
◦ Attacks that involved only a few total packets
◦ Few services were running on connected hosts
(mostly laptops)
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Natural load-balancing
◦ Port scans that were distributed over hosts on all 30
access points
◦ Backscatter from DoS attacks throughout the
Internet that produced unsolicited TCP SYN ACKs,
resets, and ICMP replies also distributed over all 30
access points
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Ideal for studying effects of malware attacks
◦ All packets are broadcasted and processed by a
single access point
◦ Broadcasts impact nearby hosts
 Channel Busy-time/Utilization
 Packet collisions
 Management frames
 Data frames
◦ Transmission rates
 Auto-Rate Fallback (ARF) mechanism
 Reduces transmission rates in favor of more robust
modulation and coding schemes
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Increased
◦ Number of data retransmissions
◦ Channel utilization
◦ Probe requests
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Reduced
◦ Transmission rates
 11-18Mbps rates increased while 48-54Mbps rates
decreased significantly
◦ Probe responses
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ICMP ping in combination with a NetBIOS
worm exploit that originated from a single
machine on the wireless LAN
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78,295 overall packets in about 18 minutes
Start:
17:02:38
End:
17:20:45
Attack halted for about 2 minutes at 17:09:00
Bursts of 235 packets per second
Average rate of 117 packets per second
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Increased round-trip-times (RTTs)
Non-Attack
Interval
During
Attack
Percent
Increase
Average
Egress
64.7 ms
99.2 ms
53.2%
Avg
Ingress
23.4 ms
36.1 ms
54.4%
Median
Egress
41.6 ms
85.0 ms
104.3%
Median
Ingress
3.2 ms
6.8 ms
112.5%
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Malicious traffic flows have a detrimental
impact on wireless networks
◦ MAC Layer
◦ Latency/Round-trip-time
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Auto-rate fallback is not optimal during
congested intervals
The mechanism of probing for better
connectivity may only increase overall
network contention
◦ Probe responses and other management frames
may be blocked during periods of high channel
utilization
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Aggregate statistics for similar data sets
◦ IETF data sets
 58th, 60th, 62nd, 64th
◦ Trend Analysis
 Malicious flows
 Evolution of malware
 Backscatter analysis
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Network Protection Solutions
◦ How to filter this traffic? How much of an impact
will this make?
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Traffic Modeling with Malicious Flows
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Contact Information
◦ Email: bstone@cs.ucsb.edu
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